This invention is in the field of optical detectors for small physical motions. Perhaps the oldest such detector is the mirror galvonometer, wherein small angular movements of a mirror carried by a galvonometer coil are detected by reflecting a spot of light off the mirror onto a relatively distant scale. Nowdays, small linear movements may be detected by such devices as the Michaelson interferometer. The instant invention is able to detect simultaneously both linear and rotational or angular movements. Moreover, the rotational motion is detected to a much finer degree than has been previously achieved.